1. Field of the Invention
This invention relates to the connection of optical fibers.
2. Description of the Prior Art
Multiplex optical fiber communication systems, utilizing fibers that carry separate channels of information, require an efficient connecting means for joining individual fibers so that light can be transmitted from one to the other. If excessive losses are encountered at the connector, the entire system becomes impractical. In the past, efforts at fiber connection primarily have involved the butting of the ends of the fibers together, along with a suitable aligning and holding means, in an attempt to cause most of the light from the emitting fiber to be received in the core of the receiving fiber. These prior devices generally have been in the nature of laboratory models rather than practical, commercially usable connectors. Major losses in making butt-joint connections are incurred from transverse fiber misalignment, end separation of the fibers, angular fiber misalignment and Fresnel reflections. These factors present such formidable design problems that heretofore there has been no fully satisfactory optical fiber interconnecting device for joining individual optical fibers.
A further problem arises in the connection of light emitting sources to the optical fiber, as well as connection of the optical fiber to a light sensitive detector. Typically, sources are designed to meet the specific requirements of the fiber optic communication systems, and hence come in many configurations. Some of these requirements are power, radiance patterns, modulation characteristics, emitting area, and spectral characteristics. These sources are typically light emitting diodes (LED) or laser diodes (LD). Some of these sources have radiance characteristics with spatial and angular distributions that are much larger than the respective receiving fiber core area and acceptance angle. Direct fiber positioning results in inefficient coupling because of the spatial and angular mismatch. Other sources have radiance characteristics that have spatial distributions smaller than the receiving fiber core area with angular distribution that extends to angles larger than the acceptance angle of the fiber. The sources of the latter characteristic are inefficiently coupled by direct positioning of the fiber because much of the light impinging upon the receiving fiber will be at an angle greater than its maximum acceptance angle and so will not be trapped in this fiber and will be lost to the system.
At the output end of the optical fiber communication system, the light sensitive detectors also come with a variety of characteristics, and again, each detector is optimized for the requirements of the communication system. Systems which require high frequency response and high sensitivity are likely to use a detector which has a very small area. If the detector area is of the order of magnitude of the emitting fiber core area or smaller, direct positioning of the fiber becomes inherently inefficient.